Optical devices, such as junction lasers, photodiodes, or light emitting diodes, are sensitive to moisture and other atmospheric contaminants. In an optical communications system employing these devices as transmitters and receivers, a hermetic housing is generally provided for their protection. Inasmuch as optical signals exit or enter the housing via optical fibers, some means to hermetically seal the fiber to the housing is required. FIG. 4 is illustrative of a hermetic package where an optical fiber-to-metal seal is utilized.
However, joining two disparate materials such as metal and glass is a difficult task, particularly in view of the large discrepancy in their coefficients of thermal expansion. The difficulty is further complicated by the fact that the mechanical and optical properties of the optical fiber must not be significantly changed during construction of the seal. Consequently, the prior art has proposed various complicated processes for hermetically sealing an optical fiber to metal. Typically, a metallic coating is sputtered on the fiber before fusing with the metal. Another technique involves depositing a glass layer on the metal's surface where it will form a bond with metallic oxides. Then this glass layer is melted onto the fiber.
A less complicated technique, disclosed in copending patent application Ser. No. 667,961, filed for I. Camlibel et al on Mar. 18, 1976 and assigned to the assignee hereof, hermetically seals an optical fiber to a metal tube, by threading the fiber through the tube, filling the tube with molten solder, and allowing it to cool. The solder, upon solidifying, squeezes the fiber and forms a hermetic seal.